1. Field of the Invention
This invention relates to a webbing lock mechanism for use in a seatbelt system for locking a webbing for restraining an occupant as necessary, and more particularly to a webbing lock mechanism in which the intermediate portion of the webbing is directly locked.
2. Prior Art
With the webbing lock mechanism used in a seatbelt system, even after the wind-off rotation of the wind-up shaft is locked, the condition of loosely wound-up webbing takes place before the webbing wound up to the wind-up shaft in layers is tightly wound up, thus causing a considerable amount of webbing to be extended out.
Then, there has been proposed a webbing lock mechanism as shown in FIG. 1, in which the intermediate portion of the webbing is directly locked by use of tensile force of the webbing when tension of the webbing is increased.
Namely, FIG. 1 is an explanatory view showing the condition of the conventional webbing lock mechanism being built in the webbing retractor 1. A frame 2 of the webbing retractor 1 is solidly secured to a vehicle body 4 by means of mounting bolts 3. A wind-up shaft 5 rotatably supported on the frame 2 winds up one end of a webbing 6 in layers, the other end of the webbing 6 is withdrawn to outside to reach an occupant restraining portion, and the wind-up shaft 5 is biased in the wind-up direction indicated by an arrow A in FIG. 1 by the biasing force of a spiral spring not shown. Further, a ratchet wheel 7 is secured to the wind-up shaft 5, and a pawl 8 being opposed to the ratchet wheel 7 and tiltably supported by the frame 2 is actuated by an acceleration sensor such as a pendulum not shown, and adapted to prevent the wind-off rotation of the webbing 6 through the mesh with the ratchet wheel 7.
Furthermore, secured to the lower portion of the frame 2 is a fixed base 9, at one side of which is provided a support shaft 10. A roller 11 around which the webbing 6 is wound is rotatably supported on the support shaft 10, on which is pivotally supported a lock lever 12. Provided at the forward end portion of the lock lever 12 is a support shaft 13, on which is rotatably supported a roller 14 around which the webbing 6 is wound. The intermediate portion of the lock lever 12 is formed into a lock portion 15. Inserted through a space between the fixed base 9 and the lock portion 15 is the intermediate portion of the webbing 6. During normal running condition of the vehicle, the webbing 6 is not clamped and smoothly slidable by the action of a leaf spring 16 for causing the lock portion 15 of the lock lever 12 to be separated from the fixed base 9, and in an emergency of the vehicle, such as a collision, the webbing wind-off rotation of the wind-up shaft 5 is suddenly stopped through the mesh between the pawl 8 and the ratchet wheel 7 due to the action of the acceleration sensor not shown, and the tension of the webbing 6 increased by the collision inertial force of the occupant makes the lock lever 12 to pivotally move about the support shaft 10, whereby the intermediate portion of the webbing 6 is clamped between the fixed base 9 and the lock portion 15 of the lock lever 12. Namely, the intermediate portion of the webbing 6 is directly locked, whereby the condition of loosely wound-up webbing 6 does not take place, so that the occupant can be placed under a condition uniformly restrained by the webbing 6.
However, in said conventional webbing lock mechanism, the lock portion 15 of the lock lever 12 approaches the fixed base 9 in rotating condition but not in parallelly moving condition, whereby the surface pressure caused in a space between the fixed base 9 and the lock portion 15 becomes non-uniform in the direction of the webbing being inserted. As the case may be, the webbing 6 is not perfectly clamped, and such problems may be encountered that the webbing 6 may slide or may be broken off by being firmly clamped only at a portion of the surface clamped by the fixed base 9 and the lock portion 15.